Fig. 8. Schematic diagrams of the hypothesis that injured deep tissue rather than skin induces spontaneous activity in the nociceptive pathways. (A ) An incision in skin only (epidermis and dermis) induces minimal spontaneous activity in nociceptors and dorsal horn neurons, which receive cutaneous input. (B ) An incision including skin and deep tissue (fascia and muscle) produces robust spontaneous activity in muscle-innervating nociceptors and the dorsal horn neurons receiving input from the muscle.